Question

A neutral water molecule $\left(H_{2}O\right)$ in its vapour state has an electric dipole moment of $2\times {10}^{-24}C-m.$ If the molecule is placed in an electric field of $2\times {10}^{4}N{C}^{{}_1}$ , the maximum torque that the field can exert on it is nearly.

• A. $4\times {10}^{-20}N-m$
• B. $6\times {10}^{-20}N-m$
• C. $8\times {10}^{-20}N-m$
• D. $2\times {10}^{-18}N-m$

Answer 1

The correct option is A $4\times {10}^{-20}N-m$

$P=2\times {10}^{-24}Cm$

$E=2\times {10}^{4}NC$

$\tau =EP=2\times {10}^{-24}\times 2\times {10}^4=4\times {10}^{-20}Nm$